During operation of a radar system over a targeted radiation reflective surface such as terrain or seawater, the radar energy emitted from the transmitter is reflected from the targeted surface along a forward scattering path toward the receiver. The radar energy is also directly transmitted to the receiver along a line-of-sight path. Typically radar frequency measurement is calibrated for a mono-static type of radar system, wherein the targeted surface is illuminated by the emitted radar energy radiation a known distance from the transmitter and the collocated receiver. Such measurement calibration is however difficult to perform for a bi-static type of radar system, especially when the target surface is close by, because the radar radiation when impinging on the targeted surface it is scattered so as to corrupt the measurement calibration process. It is therefore an important object of the present invention to facilitate radar frequency calibration for the bi-static type of radar system.